Field of the Invention
The present invention relates to a solar cell, particularly a solar cell having a protective layer.
Solar cells have attracted attention as an energy supply means since they are free from the problem of air pollution occurring in thermal or nuclear electric power generation and electric energy can be obtained at any location where solar energy is available.
Under the existing circumstances, however, the production (or manufacturing) cost of solar cells is high and the conversion efficiency (or energy conversion efficiency) thereof is not always satisfactory. In addition, solar cells have a problem in durability, so that solar cells are not widely popular at the present stage. In order to further popularize the solar cell, long-term outdoor durability, in addition to an improvement in the conversion efficiency, is required. A protective layer plays an important part in improving durability and reliability of solar cells under such conditions.
Further, an electrode constituting a solar cell unit is generally liable to be oxidized by moisture, so that it is preferable that the solar cell be sheltered from the outside by the medium of a protective layer to improve moisture resistance, weathering resistance, etc.
There have been proposed a protective layer for a conventional solar cell comprising a resin film such as a polymethylmethacrylate or epoxy resin film (Japanese Laid-Open Patent Application No. (JP-A) 88481/1985), a silicone resin film (French Patent No. (FR) 2426337), or a fluorine-containing resin film (JP-A 73942/1984).
These protective layers, however, inherently have an insulating property, and so dust or dirt is liable to adhere to or cover the surface of such protective layers. As a result, light transmission of the conventional solar cell is hindered, thus lowering the conversion efficiency in some cases.